1. Field of the Invention
This invention concerns an improved fundus camera which can take photographs other than by fluorescence (black and white, or color), and by fluorescence.
2. Description of the Prior Art
A fundus camera is known in the art wherein, except when taking photographs other than by fluorescence (black and white or color), a subject may be given an intravenous injection of the fluorescent agent fluorescein. The fundus of the subject's eye is illuminated by light in the visible wavelength region so as to excite this fluorescent agent and a photograph is taken by the fluorescence of the fluorescent agent. In this type of fundus camera, a photograph may also be taken by giving the subject an injection of the fluorescent agent indocyanin green and illuminating the fundus by light in the infra-red region so as to excite the fluorescent agent.
In this type of fundus camera, an annular diaphragm is provided as a stop in the illuminating optical system, this annular diaphragm being disposed in a substantially conjugate position to the front portion of the eye undergoing examination, and the illuminating light is guided to the eye via the diaphragm. The illuminating light becomes ring-shaped in the vicinity of the pupil of the eye, and this ring-shaped illumination is guided to the fundus through the periphery of the pupil so as to illuminate the fundus. For the purpose of observing the eye, this illuminating light is visible light. The light reflected by the fundus is then guided to observation and photographic optical systems through the central region of the pupil. The photographer first selects the part of the fundus it is desired to photograph, and then selects an appropriate photographic mode. When exciting a fluorescent agent in order to photograph the fundus, an exciter filter which passes only light of specific wavelengths is inserted in the optical path of the illuminating light. Further, a barrier filter which essentially transmits only the fluorescence emitted by the fluorescent agent due to excitation by the illuminating light, is inserted in the optical path of the photographic optical system.
As only specific wavelengths in the illuminating light are used when taking photographs by exciting the fluorescent agent, higher light intensities have to be used than when taking photographs other than by fluorescence.
In this conventional fundus camera, however, the fundus of the eye under examination is illuminated by a ring-shaped illumination obtained using a single annular diaphragm. The amount of light passing through this diaphragm was insufficient, and consequently, good observations and photographs could not be obtained by fluorescence. Further, if the fundus were illuminated by infra-red light to excite the fluorescent agent, an even greater amount of light is required.